As a terrestrial digital broadcast standard, for example, there is Digital Video Broadcasting-Terrestrial 2 (DVB-T2). In DVB-T2, a modulation scheme called an orthogonal frequency division multiplexing (OFDM) scheme is used.
In the OFDM scheme, digital modulation such as phase shift keying (PSK) or quadrature amplitude modulation (QAM) is performed by providing several orthogonal subcarriers in transfer bands and allocating data to amplitudes and phases of the respective subcarriers.
As kinds of frames of digital signals in conformity with DVB-T2 (hereinafter also referred to as DVB-T2 signals), there are frames in conformity with DVB-T2 (hereinafter also referred to as T2 frames) and frames in conformity with standards to be regulated in the future (hereinafter also referred to as future extension frame (FEF) parts) other than DVB-T2.
A P1 signal which is a preamble is disposed at the beginning of each frame of a DVB-T2 signal.
In a T2 frame of the frames of the DVB-T2 signal, a P2 signal which is a preamble and a data signal which is a payload (user data) are disposed after the P1 signal.
Here, the P1 signal includes S1 and S2 signals. The S1 and S2 signals include a fast Fourier transform (FFT) size of a frame, communication scheme information indicating whether a communication scheme is multiple input single output (MISO) or single input single output (SISO), and type information indicating whether the frame is an FEF part.
Accordingly, since the P1 signal (the S1 and S2 signals included in the P1 signal) indicates information of a frame in which the P1 signal is included (disposed), a reception device receiving a DVB-T2 signal first detects the P1 signal from a received signal obtained by receiving the DVB-T2 signal and instantly decodes (demodulates) the P1 signal.
When a T2 frame and an FEF part are present together in a DVB-T2 signal, a reception device decoding the T2 frame (hereinafter also referred to as a T2 reception device) among reception devices receiving the DVB-T2 signal extracts and decodes only the T2 frame included in the received signal based on the type information included in a P1 signal detected from a received signal obtained by receiving the DVB-T2 signal in which the T2 frame and the FEF part are present together.
Incidentally, since there is no rule regarding content of the FEF part in the DVB-T2, it is not known which signal is disposed in the FEF part.
Accordingly, when a T2 reception device has an automatic gain control (AGC) function, there is a concern of a gain of the AGC function following a level (power) of an FEF part in a section of the FEF part (the gain of the AGC being controlled so that the power of the FEF part becomes predetermined power) and affecting a section of the T2 frame (a received signal of the T2 frame).
Thus, in the DVB-T2 Implementation Guidelines (Non-Patent Literature 1), it is proposed that the AGC function be stopped in a section of an FEF part and a gain be held at a constant value immediately before the stop.